[CHORE] Add playwright eslint plugin

- Add https://github.com/playwright-community/eslint-plugin-playwright
as a linter for the playwright tests.
- `no-networkidle` and `no-conditional-in-test` are disabled as fixing
those doesn't seem to really improve testing quality for our use case.
- Some non-recommended linters are enabled to ensure consistency (the
prefer rules).

tests/e2e/commit-graph-branch-selector.test.e2e.js

@@ -19,7 +19,7 @@ test('Switch branch', async ({browser}, workerInfo) => {
 
   await page.waitForLoadState('networkidle');
 
-  await expect(page.locator('#loading-indicator')).not.toBeVisible();
+  await expect(page.locator('#loading-indicator')).toBeHidden();
   await expect(page.locator('#rel-container')).toBeVisible();
   await expect(page.locator('#rev-container')).toBeVisible();
 });